Molded thermoset plastics are finding increased utilization as substitutes for metals in a variety of areas such as automotive parts, recreational vehicles, etc. Many of these applications are for painted parts requiring smooth surface appearance and these parts often have in-mold coatings to achieve the smoothness. These molded thermosets also use low profile additives to decrease part shrinkage during molding. The low profile additive and molding conditions can create internal porosity that can entrap air, gases, and volatile compounds. Any abrasion, cutting, or fracture of the molded parts creates disruptions of a resin rich skin on said molded part, said disruptions having enhanced surface porosity. It is known that during heated cure cycles for subsequent finish paints (coatings) on fiber reinforced thermoset parts, blemishes in the top coating, known as paint pops or craters, can develop. It is believed that gases evolving from internal porosity are creating these defects as the gases try to escape from the molded part during the heated cure cycle for the coating.
U.S. Pat. No. 5,021,297 describes heating a molded plastic part (degassing the part) and then applying a thermoset powder coating over the surfaces of the part that will be subsequently coated. To be effective this barrier needs to be substantial, 1-6 mils thick.